Transducer devices are used in a variety of applications to transfer energy between electrical systems and mechanical systems. Quartz crystal microbalance (QCM), for example, is a transducer-based technology that may employ piezoelectric transducers in various configurations to perform sensing functions. QCM technology takes advantage of the fact that the resonant frequency of a transducer typically varies with the effective mass of the transducer. Accordingly, when portions of a sample material bind to the transducer, the mass of the bonded sample material can be detected by monitoring the resonant frequency of the vibrating mass, relative to a predetermined reference.
A related technology is rupture event scanning (RES), in which transducers may be employed to produce mechanical energy to break bonds within a sample material. In addition to providing energy to break the bonds, the transducers may be used as sensors to analyze acoustic events (e.g., a pressure wave) that can occur when bonds break. Different types of bonds have unique properties that produce distinctive acoustic events. The bonds can be identified and analyzed by using various techniques to study the acoustic events.
Transducer systems such as those described above typically employ multiple distinct transducers. The transducers are often provided in an array, with some type of mechanical suspension being used to suspend the transducers in place relative to a base or other stationary component of the system.
Although many prior systems have multiple transducers, typically only one transducer can be activated at any given time. Alternatively, where multiple transducers are simultaneously active, the activated transducers commonly must be separated by a relatively large physical distance. The reason for this is to avoid undesired signal coupling that can occur when physically proximate transducers are active at the same time.
One type of undesired coupling results from the liquid that is often used to hydrate biological samples in QCM and RES applications. Where a well of liquid is spread across multiple transducers, or even where separate liquid wells are employed for each transducer in a multiple-transducer configuration, mechanical vibration produced by one transducer can be transmitted through the liquid (and through intervening structures) to other transducers in the system. Accordingly, when the transducers are simultaneously activated, the electrical signal produced at the second transducer will include interference produced by the vibration of the first transducer. The mechanical suspension that holds the transducers in place can also transmit vibration from one transducer to another, even though such suspensions typically are designed to minimize this effect. Finally, stray capacitance, stray mutual inductance and other indirect electrical coupling can produce interference when physically proximate transducers are activated simultaneously.
Because prior systems typically do not provide for simultaneous activation of physically proximate transducers, they may be limited in processing speed and may not be able to provide a satisfactory level of performance in applications where it is desirable to operate multiple transducers at the same time.
In some prior systems, resolution is limited by the drive signal used to activate the transducers. In particular, the fabrication process and other factors may lead to variations in the resonant frequencies of the transducers in the system. Failure to accommodate these variations can diminish the resolution and/or accuracy of the sensor system. Specifically, when a transducer is activated at frequencies other than its resonant frequencies, the resulting vibration will be less than the maximum possible amount. This can result in lower resolution output signals that are more susceptible to noise.
Other transducer-based sensor systems and methods suffer from disadvantages relating to impedance within the output signal paths for the transducers. In many cases, the impedances within the output signal paths are matched for only a narrow range of output signals. As a result, mismatches and incomplete terminations occur when output signals have characteristics falling outside this range (e.g., frequencies that are higher or lower than the expected range of output frequencies). The signal reflections and other artifacts that can result from the impedance mismatches can significantly complicate the processing of output signals, and can hinder rejection of unwanted noise components.